Sure you can use that kind of rationale to justify immoral and stupid actions, but in this specific context it was a completely rational action.
Someone else was going to build a nuclear bomb eventually (at the time time the Manhattan project began, the US was worried Germany would). Unless the US wanted someone else to have a massive advantage over them, the only rational choice was to build nuclear weapons.
Do you believe that no other country would have developed nuclear weapons if the US didn't?
Let's say Russia had nuclear capabilities and the US didn't? Would Russia have used them as leverage against the US? Of course they would have.
>but Gorbachev let go. Was that rational within your framework?
First, this isn't really relevant. Gorbachev kept his nuclear arsenal and military mostly intact, and thus was protected against potential foreign aggression.
Second, that's a very simplistic view of what happened. Gorbachev didn't want to completely dissolve the USSR, he just realized that in it's current form it wasn't working. He wanted to modernize communism, but he completely lost control of his reform. His eventual plan was to form a new union, but the Ukrainian Referendum made that unlikely, and then Yeltsin forced him out of power.
It's also very unlikely the USSR could have evolved into anything like North Korea--mainly because Russia was much more developed than North Korea, much larger, and had a much larger population.